1. Field of the Invention
The present invention relates to a heating device using induction heating, particularly to a fixing device which is usable in a copying device or a printer device of an electrophotographic system using a hot-melting developer and which fixes the developer on a recording object.
2. Description of the Related Art
In a fixing device incorporated in a copying device using an electrophotographic process, a toner (developer) formed on a material to be fixed (recording material) is heated and molten to fix the toner on the recording material. In recent years, induction heating has been broadly used as a heating system capable of reducing heating time which is a time from a time when power supply is started until temperature reaches a fixable temperature. However, in induction heating, it is known that an interference sound is generated in a case where there are a plurality of coils as magnetic flux generation device and frequencies of powers supplied to individual coils differ. When a heating object is a roller body, it is difficult to maintain a certain distance between each coil and the roller body. It is also known that the coil is disposed along the peripheral surface of the roller body in order to maintain a certain distance between each coil and the roller member, and it is accordingly difficult to keep a certain magnetic flux density.
For example, in Jpn. Pat. Appln. KOKAI Publication Nos. 2003-86344 and 2003-215957, an attempt is described to increase a space (spatial distance) between the roller body which is the heating object and each electric wire of the coil used in a heating device while securing a magnetic flux density capable of reaching the roller body.
For example, in Jpn. Pat. Appln. KOKAI Publication No. 2002-222687, it is described that a magnetic flux distribution adjustment member is disposed to compensate for the magnetic flux density decreasing when each electric wire of the coil body of a heating device is disposed along the peripheral surface of the roller member as the heating object.
For example, in Jpn. Pat. Appln. KOKAI Publication No. 2002-34241, it is proposed that two systems of circuits for supplying powers to a plurality of coil bodies are disposed. In a first circuit, a time for supplying the power to the coil body connected to the first circuit is changed. In a second circuit, the power is supplied to the coil body connected to the second circuit at the same frequency as that for use in the first circuit for a period for which no power is supplied to the coil body connected to the first circuit.
However, even by any of the proposals described in the above-described documents, the temperature of the roller body which is the heating object is not uniformed in a whole region of the roller body in a longitudinal direction. Moreover, in a method of supplying the powers having different frequencies to the coils using a plurality of coil bodies, reduction of the interference sound is not realized while reducing cost required for a circuit which supplies the powers.